This invention relates to an apparatus and process for harnessing energy from ocean waves. More particularly, this invention relates to an apparatus and process for utilizing the changing hydrodynamic pressure of ocean waves to generate electrical power.
It is well known that ocean waves represent a large untapped reservoir of renewable energy sources. However, the technology for harnessing energy derived from ocean waves is still in the very early stages of development and suffers many problems from the standpoint of economical and practical utilization.
By far, the largest number of prior art devices which have attempted to harness energy from ocean waves have involved the use of devices which float or operate on the surface of the ocean to produce a mechanical generator-operating action through gearing or the like as described in Masuda U.S. Pat. No. 3,204,110, or to compress atmospheric air entrapped above the wave crests to operate an air motor driving the electric generator as in Corbett Jr. et al U.S. Pat. No. 3,064,137. Other examples of surface wave energy machines are described in the IEEE spectrum article of September 1979 pages 42-49.
However, such surface based devices suffer from several important problems, chief among those problems is the fact that the turbulent forces from even a moderate sea, let alone a stormy sea, will cause such surface devices to suffer considerable damage or be destroyed. As a consequence, enormous costs are involved due to repair and replacement.
Clearly, a reasonable alternative to surface wave energy devices would be to utilize a device which harnesses the energy from ocean waves and is submerged beneath the ocean so as to avoid the harsh environment at the surface. One such apparatus is described in U.S. Pat. No. 3,353,787 to Semo. In Semo, a closed hydraulic system is presented employing an array of submerged fixed-position tubes extending parallel to a shoreline and having flexible upper surfaces for downward deflection by overhead wave pressure to displace hydraulic fluid into a collecting conduit leading to a shore installation that includes an accumulator. The Semo apparatus also includes a hydraulic motor for generator operation and a return sump at exit to the motor. Return flow of hydraulic fluid to the submerged tubes is intended to occur via the above collecting conduit. A check valve at each tube permits facile egress of fluid from such tube and a restricted port through each check valve is intended to permit slow return flow to each tube for refilling. While a submerged closed-circuit power generating system of the fixed-position flexible-wall fluid-displacement type can have the advantage of allowing the ocean surface to remain unobstructed while at the same time affording a breakwater action for shoreline protection, the practical operability of the Semo apparatus is questionable with respect to displacement of hydraulic fluid by wave-created subsurface pressure variation, as well as with respect to the facile-egress restricted-return flow to and from the tubes imposed by the choked check valves in the Semo system.
Another example of a submerged wave energy power generating device is disclosed in U.S. Pat. No. 3,989,951 to Lesster et al. In Lesster et al, a breakwater apparatus which generates electrical power by extracting energy from sea waves is provided. The apparatus consists of an array of subsurface fixed-position flexible-wall pneumatic bags or cells, and a closed cycle system which reacts to surface wave correlated static pressure variations by expiring compressed gas into a supply header to a generator driving a pneumatic motor while simultaneously expiring return gas in a return header from the motor. Alternate inspirational-expirational operation of individual cells involves use of a supply check valve at each cell, discharging it to the supply header, and a return check valve at each cell, receiving from the return header.
While overcoming some of the problems inherent with the above discussed Semo device, the Lesster et al apparatus also suffers from several disadvantages and deficiencies. For example, the apparatus must be kept absolutely level in the presence of ocean waves or all the air will go to the highest bag resulting in the collapse of the lowest bag. Also, the pressure in the supply duct to the turbine is an average of the highest pressure experienced by the bag. Similarly, the pressure in the return duct is an average of the lowest pressure experienced by the bags. As a result, the efficiency of power generated from any given wave will be relatively low with the Lesster et al apparatus.
Other prior art patents of interest with respect to submerged ocean wave energy devices include U.S. Pat. No. 3,598,505 to Green et al and U.S. Pat. No. 4,145,882 to Thorsheim.